1. Field of the Invention
The present invention relates to a substrate holder for use in a plating apparatus for carrying out plating of a surface (front surface) to be plated of a substrate, in particular a plating apparatus for forming a plated film in fine interconnect trenches and holes, or resist openings, provided in a surface of a semiconductor wafer, or for forming bumps (protruding electrodes), which are for electrical connection to, e.g., electrodes of a package, on a surface of a semiconductor wafer. The present invention also relates to a plating apparatus provided with the substrate holder.
2. Description of the Related Art
It is common practice, e.g., in TAB (tape automated bonding) or flip chip to form protruding connection electrodes (bumps) of gold, copper, solder or nickel, or of multiple layers of such metals at predetermined portions (electrodes) of a surface of a semiconductor chip, having interconnects formed therein, so that the semiconductor chip can be electrically connected via the bumps to electrodes of a package or TAB electrodes. There are various methods usable for the formation of bumps, such as electroplating, vapor deposition, printing and ball bumping. Of these, electroplating, which can form fine bumps and can be performed in a relatively stable manner, is most commonly used as the I/O number of a semiconductor chip increases and the electrode pitch becomes smaller.
Electroplating methods can be classified roughly into a jet method or cup method in which a substrate, such as a semiconductor wafer, is held in a horizontal position with a surface to be plated facing downwardly, and a plating solution is jetted upwardly onto the surface to be plated, and a dip method in which a substrate is held in a vertical position in a plating tank, and a plating solution is injected upwardly into the plating tank and the plating solution is allowed to overflow the plating tank during plating. Electroplating using a dip method has the advantages of a small footprint and good release of bubbles which adversely affect the quality of plating, and is therefore considered suited for bump plating in which plating is performed for relatively large-sized holes and which requires a considerably long plating time.
A common conventional electroplating apparatus using a dip method, which has the advantage of good release of bubbles, is provided with a substrate holder which detachably holds a substrate, such as a semiconductor wafer, with its front surface (surface to be plated) exposed while sealing an end surface and a back surface of the substrate. The substrate holder, together with a substrate, is immersed in a plating solution in carrying out plating of the surface of the substrate.
With the recent development of those devices and packaging processes which use plating, there is a need to process not only a semiconductor wafer having a standard thickness (775 μm) but also substrates having various diameters. A demand therefore exists for the development of a substrate holder suitable for limited production of diversified products in which processing of substrates having various diameters is required.
A substrate holder, which is to be immersed in a plating solution, needs to securely seal a periphery and a back surface of a substrate so that the plating solution will not enter the back surface of the substrate when the substrate holder holds the substrate. The applicant has proposed a substrate holder for detachably holding a substrate between a first holding member (fixed holding member) and a second holding member (movable holding member) while pressing a substrate sealing member (inner sealing member), mounted to the second holding member, against a peripheral portion of the substrate to seal the contact portion and pressing a holder sealing member (outer sealing member), mounted to the second holding member, against the first holding member to seal the contact portion (see, e.g., patent documents 1 and 2).
In such a substrate holder, the amount of compression of a substrate sealing member for pressing on and sealing a peripheral portion of a substrate changes with the different thickness of the substrate. When the amount of compression of the substrate sealing member is small, there is a fear of leakage of a plating solution. When the amount of compression of the substrate sealing member is large, there is a fear of breakage of a substrate, sticking of the substrate sealing member to a substrate, etc. Further, a change in the thickness of a substrate leads to a change in the contact force on a substrate of an electrical contact which, when the substrate is held by the substrate holder, makes contact with the substrate to supply electricity to the substrate. A small contact force of the contact on a substrate results in a large contact electrical resistance upon supply of electricity to the substrate, whereas a large contact force of the contact on a substrate can cause a scratch in the substrate.
A substrate holder for detachably holding a substrate while absorbing variation (change) in the thickness among substrates has been proposed which includes a leaf spring, disposed in a recess provided in the substrate holder, for biasing a substrate in a direction away from the recess (see patent document 3). To dispose a plate between the leaf spring and a substrate has also been proposed (see patent document 4). A substrate holder has been proposed in which a substrate is pressed against a jig by the biasing force of a spring to obtain a sealing force of a sealing member, mounted on the jig, on a peripheral portion of the substrate (see patent document 5). A substrate holder has been proposed in which a substrate, supported by a support plate, is pressed against a sealing member by the biasing force of a compression spring so that the amount of compression of the sealing member upon pressure contact with a peripheral portion of the substrate is substantially constant regardless of the thickness of the substrate (see patent document 6). A substrate holder has also been proposed which is configured to be capable of applying a constant pressing load, without an adjustment, to a substrate from the back surface by means of a pressing member which is pressed by the biasing force of a compression spring (see patent document 7).